Battery status monitoring apparatus and method

ABSTRACT

A microcomputer  23  monitors the battery condition by detecting a first deterioration degree caused by increase of an internal resistance of a battery  13  and a second deterioration degree caused by inactivation of an activation material in the battery  13  based on outputs of a current sensor  15  and a voltage sensor  17.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a battery deterioration degree monitor and amethod of that, especially a battery deterioration degree monitor formonitoring deterioration degree of the battery and a method of that.

2. Description of the Related Art

The battery for a vehicle installed in the vehicle is applied widely asan electric power source for engine starting or operation of electricdevices in the vehicle. Therefore, recognizing charge condition of thebattery is very important.

When repeating charge-and-discharge in the battery, a terminal voltageof the battery is gradually decreased. Therefore, for recognizingsecurely the charge condition, it is a very important object torecognize the latest deterioration condition (deterioration degree) ofthe battery. Usually, by detecting a direct-current resistance (ohmicresistance) of the battery, as a part of the internal resistance whichis not changed by a discharge current or a discharge time, thedeterioration degree to be an indicator of deterioration is obtainedbased on the detected direct-current resistance.

SUMMARY OF THE INVENTION

Objects to be Solved

As causes of increasing the internal resistance of the battery, thereare reversible deterioration generated temporarily by temperature changeand irreversible deterioration generated by that inactivation of anactive material caused by corrosion of a lattice, sulfation and drop ofthe active material during repeat of charge/discharge.

Therefore, by monitoring the deterioration to cause increase of theinternal resistance, the deterioration including the reversibledeterioration and the irreversible deterioration mentioned above can bemonitored. However, by monitoring only the deterioration to causeincrease of the internal resistance, the irreversible deteriorationgenerated by repeat of charge/discharge cannot be monitored, so that thebattery condition cannot be monitored securely.

To overcome the above problem, objects of the present invention are toprovide a battery condition monitor, which can monitor a batterycondition securely and a method of monitoring the battery condition.

How to Attain the Object of the Present Invention

In order to attain the object, a battery condition monitor formonitoring a condition of a battery according to claim 1 of the presentinvention includes a first deterioration detector for detecting a firstdeterioration degree cause by increase of an internal resistance of thebattery, and a second deterioration detector for detecting a seconddeterioration degree caused by decrease of active material of thebattery to cause decrease of a charge capacity of the battery, and thecondition of the battery is monitored based on the first deteriorationdegree and the second deterioration degree.

A method of monitoring a battery condition according to claim 4 of thepresent invention has a step of monitoring the battery condition basedon a first deterioration degree caused by increase of an internalresistance of the battery and a second deterioration degree indicating adecreasing value of active material of the battery to cause decrease ofa charge capacity of the battery.

According to claim 1 or 4 of the present invention, the firstdeterioration degree caused by increase of the internal resistance ofthe battery and the second deterioration degree caused by decrease ofthe active material of the battery to cause decrease of the chargecapacity of the battery are monitored. The condition of the battery ismonitored based on the first deterioration degree and the seconddeterioration degree. The deterioration including the reversibledeterioration and the irreversible deterioration can be monitored by thefirst deterioration degree, and the irreversible deterioration can bemonitored by the second deterioration degree.

The battery condition monitor according to claim 2 of the presentinvention is characterised in the battery condition monitor as claimedin claim 1, in that the first deterioration detector obtains adirect-current resistance of the battery based on a discharge currentand terminal voltage of the battery detected in a high-rate discharging,and obtains a saturated polarization, as a saturated value of a voltagedrop by the internal resistance other than the direct-current resistanceof a terminal voltage, based on the discharge current and the terminalvoltage of the battery detected in discharging, and the direct-currentresistance of the battery, and detects the first deterioration degreebased on the direct-current resistance and the saturated polarization.

According to claim 2 of the present invention, the first deteriorationdetector obtains the direct-current resistance of the battery based onthe discharge current and terminal voltage of the battery detected inthe high-rate discharging, and obtains the saturated polarization, asthe saturated value of a voltage drop by the internal resistance otherthan the direct-current resistance of a terminal voltage, based on thedischarge current and the terminal voltage of the battery detected indischarging, and the direct-current resistance of the battery, anddetects the first deterioration degree based on the direct-currentresistance and the saturated polarization.

Therefore, only by detecting the discharge current and the terminalvoltage of the battery in various discharging, and processing detectedresults, the direct-current resistance and the saturated polarizationcan be obtained. By obtaining the saturated polarization, the firstdeterioration degree at a point, which a dischargeable capacitydecreases to the smallest when the discharge continues, can bemonitored.

The battery condition monitor according to claim 3 of the presentinvention is characterised in the battery condition monitor as claimedin claim 1 or 2 in that the second deterioration detector detects thesecond deterioration based on the decreasing value of the chargecapacity at full-charge of the battery at any time corresponding to thecharge capacity at full-charge of the new battery.

According to claim 3 of the present invention, the second deteriorationdetector detects the second deterioration based on the decreasing valueof the charge capacity at full-charge of the battery at any timecorresponding to the charge capacity at full-charge of the new battery.Therefore, by obtaining the decreasing value of the charge capacity atfull-charge, the second deterioration degree can be easily obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of a battery conditionmonitor performing a method of detecting a dischargeable capacity and amethod of monitoring a battery condition according to the presentinvention;

FIG. 2 is a graph showing one example of a discharge current with a rushcurrent at starting of driving a starter motor;

FIG. 3 is a graph showing an example of characteristics of 1-V by anapproximate quadratic equation;

FIG. 4 is a graph showing an example of method of deleting a part byconcentration polarization from an approximate equation of increasing;

FIG. 5 is a graph showing an example of a method of deleting a part byconcentration polarization from an approximate equation of decreasing;

FIG. 6 is a graph showing an example of characteristics of 1-V by anapproximate linear equation of increasing;

FIG. 7 is a graph showing an example of the other method of deleting apart by concentration polarization from an approximate equation ofdecreasing;

FIG. 8 is a graph showing an example of a furthermore method of deletinga part by concentration polarization from an approximate equation ofdecreasing;

FIG. 9 is a graph for explaining a method of obtaining a saturatedpolarization in discharging in a balanced condition or a conditionhaving discharging polarization.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of a battery condition monitor acting a method ofmonitoring a battery condition according to the present invention willbe described with reference to figures. Before that, a method ofobtaining a direct-current resistance of the battery will be describedfor calculating a first deterioration degree (call SOH1 hereafter) tocause increase of an internal resistance of the battery.

In a 12V car, a 42V car, an EV car and an HEV car having a battery, aconstant load such as a starter motor, a motor generator and a drivemotor, which requires large current, is installed as a vehicle loadacting by supplied power from the battery. When a large current constantload like the starter motor is turned ON, after a rush current flows inthe constant load, a constant current corresponding to a value of theload flows. When the load is a lamp, the rush current is called aninrush current.

When a direct-current motor is applied to the starter motor, the rushcurrent flowing in a field coil increases from zero to a peak value asfew times large as that of the constant current, for example 500 [A],monotonously in a short time such as 3 msec. just after starting drivingthe constant load as shown in FIG. 2. After that, the current decreasesfrom the peak value to the constant value corresponding to the constantload monotonously in a short time such as 150 msec. Thus, the current issupplied as a discharge current by the battery. Therefore, by measuringthe discharge current of the battery and a terminal voltagecorresponding to the discharge current when the rush current flows inthe constant load, characteristics of the discharge current (I) of thebattery and the terminal voltage (V), which shows a change of theterminal voltage against a wide-range change of the current from zero tothe peak value, can be measured.

The battery is discharged by an electronic load, in which the currentincreases from zero to 200[A] in 0.25 sec. and decreases from the peakvalue to zero in the same time, as a approximated dischargecorresponding to the rush current flowing when the starter motor isturned ON. By measuring a pair of the discharge current of battery andthe terminal voltage in a short constant period, and plotting themeasured pair of data to correspond the discharge current to ahorizontal axis and the terminal voltage to a vertical axis, a graphshown in FIG. 3 is given. The characteristics of the current-voltage inincreasing and decreasing discharge current shown in FIG. 3 can beapproximated to flowing quadratic equations by a least squares method.V=a1*I ² +b1*I+c1  (1)V=a2*I ² +b2*I+c2  (2)

In FIG. 3, curves of approximated quadratic equations are drawn tooverlap on.

In FIG. 3, a voltage difference (c1−c2) between an intersection point ofthe approximated curve of increasing current and an intersection pointof the approximated curve of decreasing current is a voltage differenceat no current of zero [A]. Then, the voltage difference is considered asa voltage drop caused only by a part by the concentration polarizationnewly occurred by discharging, not including the direct-currentresistance and the activation polarization. Therefore, the voltagedifference (c1−c2) is caused only by the concentration polarization, andthe concentration polarization at the current of zero [A] is calledVpolc0. Any concentration polarization is considered as a value ofmultiplying a current value and a time of current flowing together,which is in proportion to A*h (or A*sec because of short time)

A method of calculating a concentration polarization at the peak currentby using the concentration polarization at the current of zero [A]Vpolc0 will be described. The concentration polarization at the peakcurrent is called Vpolcp. Vpolcp is shown by the following equation.Vpolcp=[(A*sec at increasing current)/(A*sec at total time fordischarging)]*Vpolc0  (3)

A*sec at total time for discharging is shown by the following equation.A*sec at total time for discharging=(A*sec at increasing current+A*secat decreasing current)

By adding the concentration polarization Vpolcp at the peak value ascalculated above to the voltage at the peak value of increasing currentof equation (1), the part by the concentration polarization at peakvalue is deleted as shown in FIG. 4. A voltage after deleting the partby the concentration polarization at peak value is called V1. V1 isshown in the following equation.V1=a1*Ip ² +b1*Ip+c1+Vpolcp

Ip is the current at the peak value.

An approximate equation of the characteristics of current-voltage of thedirect-current resistance and the activation polarization as shown inFIG. 4 is tentatively shown as the following equation.V=a3*I ² +b3*I+c3  (4)

Since the activation polarization and the concentration polarization atthe current of zero [A] before start of discharging is considered basedon c1, c3=c1 is given by the equation (1). Assuming that the currentincreases rapidly from an initial condition of increasing the current,but reaction of the concentration polarization is slow and the reactionis almost not proceeded, differential values of the equations (1) and(4) at the current of zero [A] becomes equal to each other so that b3=b1is given. Therefore, by substituting c3=c1 and b3=b1, the equation (4)will be rewritten as the followings.V=a3*I ² +b1I+c1  (5)

a3 is the only unknown quantity.

After that, assigning a coordinate of the peak of increasing current tothe equation (5), and straightening it about a3, the following equationcan be given.a3=(V1−b1*Ip−c1)/Ip ²  (5)

Thus, the approximate equation of the current-voltage characteristicsonly by the direct-current resistance and a part by the activationpolarization is given by the equation (5).

A method of deleting the part by the concentration polarization from thedecreasing current curve will be described as follows. An equation ofdecreasing current of the direct-current resistance and the activationpolarization can be given by the same method of deleting theconcentration polarization at the current peak value. Defining twopoints other than the peak value as points A and B, concentrationpolarization VpolcA, VpolcB at the points A and B is given by thefollowing equations.VpolcA=[(A*sec from start of increasing current to point A)/(A*sec attotal time for discharging)]*Vpolc0  (6)VpolcB=[(A*sec from start of increasing current to point B)/(A*sec attotal time for discharging)]*Vpolc0  (7)

By using coordinates of three point of two points of deleting the partby concentration polarization other than the peak value given by theabove equations (6), (7), and the peak value, a curve of decreasingcurrent of the direct-current and the activation polarization shown bythe following equation is given as shown in FIG. 5.V=a4*I2+b4*I+c4  (8)

Coefficients a4, b4, c4 in the equation (8) can be determined by solvingthree simultaneous equations by assigning the current values and thevoltages of the three points of points A, B and the peak point into theequation (8).

A method of calculating the direct-current resistance of the batterywill be described. A difference between the curve of increasing currentof the direct-current resistance and activation polarization excludingthe concentration polarization shown by the above equation (5), and thecurve of decreasing current of the direct-current resistance andactivation polarization excluding the concentration polarization shownby the above equation (8) is according to the difference of the part bythe activation polarization. Therefore, by deleting the part by theactivation polarization from the above curves, the direct-currentresistance can be given.

Watching the peak value of the both curves those the activationpolarization is the same value to each other, a differential value R1 ofincreasing current and a differential value R2 of decreasing current atthe peak value are given by the following equations.R1=2*a3*Ip+b3  (10)R2=2*a4*Ip+b4  (11)

A difference between the differential values R1 and R2 is caused by thatone is the peak value of increasing of the activation polarization andthe other is the peak value of decreasing. When the battery isdischarged by using the electronic load to discharge as increasing fromzero to 200 A within 0.25 sec and decreasing from the peak value to zerowithin the same time as a approximated discharge corresponding to therush current, the both rates of change in the vicinity of the peak valueare equal to each other, and it is considered that the characteristicsof current-voltage by the direct-current resistance exists between theboth. Therefore, by adding the differential values and dividing that by2, the direct-current resistance R can be given by the followingequation.

A case that the battery is discharged by using the electronic load asthe approximated discharge corresponding to the rush current isdescribed above. In case of actual vehicle, during the rush currentflows in the field coil, the current reaches up to the peak, andcranking is acted by a current decreased down under the half of the peakcurrent after reaching peak.

Therefore, the increasing current finishes in a short time of 3 msec.Such rapid current change almost never generate the concentrationpolarization at the peak value of the increasing current. The decreasingcurrent flows in a long time of 150 msec comparing with the increasingcurrent, so that, although decreasing current, a large concentrationpolarization is generated. During cranking, different phenomenon otherthan that during the rush current flows occurs. Discharge current andterminal voltage of the battery during cranking are not applied as datato determine the characteristics of current-voltage of decreasingcurrent.

In such condition, the increasing current in the actual vehicle can beapproximated by a straight line made with two points of a start point ofincreasing current and a peak value, as shown in FIG. 6. Generated valueof the concentration polarization at the peak value of 500 [A] can bejudged as zero [A]. In this case, a differential value at the peak valueof increasing current uses a gradient of the approximated line of theincreasing current.

In this case, a simple arithmetic average of the gradient of theapproximated line of the increasing current and a gradient of atangential line at the peak point of the approximated quadratic equationof the decreasing current cannot be applied. In such condition,generation of the concentration polarization completely differs betweento-peak and after-peak, so that an assumption that the both ratios ofchange at the peak value are the same is not realized.

The direct-current resistance in this case is obtained by multiplyingrespectively change values per a unit of a current change of twoterminal voltages at points corresponding to peak values of the firstand second change values excluding the voltage drop by the concentrationpolarization, those are gradients, and ratios of times of monotonouslyincreasing and monotonously decreasing against the total time of rushcurrent flowing, and adding the results. In short, proportional ratiosthose are distributed by the monotonously increasing time against thetotal time and the monotonously decreasing time against the total timeare multiplied with the each gradient and the result are added. Thereby,compensating an effect caused to each other by the activationpolarization and the concentration polarization, the direct-currentresistance can be obtained.

The activation polarization is generated in principal to have a valuecorresponding to the current. However, The value is affected by anamount of the concentration polarization, so that the value is notgenerated in principal. The smaller concentration polarization makes theactivation polarization smaller, and the larger concentrationpolarization makes the activation polarization larger. In any case, themiddle value between two changes per a unit of current-change of theterminal voltages at the points corresponding to the peak values of thetwo approximate equations excluding the voltage drop by the part by theconcentration polarization can be measured as the direct-currentresistance of the battery.

In a recent vehicle, an AC motor such as a magnet motor and a brushlessDC motor, which requires a three-phase input power is used morefrequently. In such motor, the rush current does not reach a peak valuein a short time. It requires approximate 100 msec and the concentrationpolarization is generated in creasing current. Therefore, as same as thesimulated discharging mentioned above, the current change curve of theincreasing current must be approximated with a curve.

When approximating the direct-current resistance and the activationpolarization at the decreasing current, for defining the peak value andtwo points other than the peak by applying the point of the current ofzero [A] as the point B as shown in FIG. 7, calculation to obtain theapproximate equation can be simplified.

If defining a point, a current of which is approximately half of thepeak current, as a point where the concentration polarization isdeleted, it can be linearly approximated to a straight line made by thispoint and the peak value. In this case, regarding the decreasingcurrent, the gradient of the approximated straight line at thedecreasing current is used as the differential value at the peak value.The direct-current resistance can be obtained accurately as same as thatby using the quadratic curve.

In short, the middle value between two changes per the unit ofcurrent-change of the terminal voltages at the points corresponding tothe peak values of the two approximate equations excluding the voltagedrop by the part by the concentration polarization can be measured asthe direct-current resistance of the battery.

In the case of using for example the starter motor, where a rush currentflowing with generating the concentration polarization at the both ofincreasing discharging current and decreasing discharging current as theconstant load, the method of measuring the direct-current resistance ofthe battery mounted on the vehicle will be described physically.

When the constant load is acted, the discharge current increasingmonotonously over a steady-state value to peak value, and decreasingmonotonously form the peak value to the steady-state value flows fromthe battery. The discharge current and the terminal voltage of thebattery at the time are sampled at intervals of for example 100micro-sec to measure them periodically, so that many couples of thedischarge current and the terminal voltage are obtained.

The latest couple of the discharge current and the terminal voltage ofthe battery obtained above are stored, memorized and collected in amemory as rewritable storage device such as a RAM in a predeterminedtime. By the least-squares method, from couples of the discharge currentand the terminal voltage stored, memorized and collected in the memory,two curved approximate equations (1) and (2) regarding to thecharacteristics of current-voltage of increasing discharging current anddecreasing discharging current which show a relation between theterminal voltage and the discharging current. By deleting the voltagedrop of the part by concentration polarization from the two approximateequations, an amended curved approximate equations excluding the part bythe concentration polarization.

The voltage difference of the approximate equations (1) and (2) at thecurrent of zero [A], flowing no current, is obtained as theconcentration polarization, not as the voltage drop by thedirect-current resistance and the activation polarization. The voltagedrop of the part by concentration polarization at the peak value at theapproximate equation (1) of characteristics of current-voltage of theincreasing discharging current is obtained with the voltage difference.For that, the fact that the concentration polarization changes by aproduct of current-time, which is given by multiplying a value ofcurrent and a time of current flowing, is used.

After the voltage drop of the part by concentration polarization at thepeak value at the approximate equation (1) of characteristics ofcurrent-voltage of the increasing discharging current is obtained, theconstant and the coefficient of a leaner term of the approximateequation including the part of the concentration polarization are madethe those of the approximate equation not including the partrespectively the same. A coefficient of a quadratic term of theapproximate equation not including the part is defined by that. Thereby,the amended curved approximate equation (5) of the approximate equationof the characteristics of current-voltage of the increasing dischargingcurrent is obtained.

After that, the approximate equation not including the part ofconcentration polarization will be given by the approximate equation (2)of the characteristics of current-voltage of the decreasing thedischarging current. For that, two points deleting the part of theconcentration polarization other than the peak value are obtained. Forthat, the fact that the concentration polarization changes by a productof current-time, which is given by multiplying a value of current and atime of current flowing, is used. When two points deleting the part byconcentration polarization other than the peak value are obtained, theamended curved approximate equation (8), which is the approximateequation (2) of characteristics of current-voltage of the decreasingcurrent amended by using three coordinates of the two points and thepeak value is obtained.

The difference between the amended curved approximate equation, shown byequation (5), of the increasing current of the direct-current resistanceand the activation polarization by deleting the part by theconcentration polarization and the amended curved approximate equation,shown by equation (8), of the decreasing current of the direct-currentresistance and the activation polarization by deleting the part by theconcentration polarization is caused by the part by activationpolarization. Therefore, the direct-current resistance can be given bydeleting the part by the activation polarization. The difference betweenthe differential values at the peak values of the increasing current andthe decreasing current is caused by that the activation polarization ofone is increasing and that of the other is decreasing. By watching thepeak values of the both approximate equations, At a middle point betweenratios of changes of the both in the vicinity of the peak value, thecharacteristics of current-voltage by the direct-current resistanceexits. Therefore, the direct-current resistance can be obtained bymultiplying the both differential values and respectively the time ratioin increasing monotonously and the time ratio in decreasingmonotonously, and adding the results.

For example, assuming that the time of the increasing current is 3 msec,and the time of the decreasing current is 100 msec, and defining thedifferential value of the increasing current at the peak value asRpolk1, and the differential value of the decreasing current at the peakvalue as Rpolk2, the direct-current resistance Rn can be calculated asfollows.Rn=Rpolk1*100/103+Rpolk2*3/103

The open-circuit voltage of the battery for the vehicle in a balancedcondition can be detected by a method of measuring the terminal voltagein an open-circuit condition of subtracting a required load to supplydark current of computer from a load acted by electric power supply fromthe battery whenever a time enough to eliminate a certaincharge/discharge polarization passes from turning an ignition switch ofthe vehicle OFF, as the latest open-circuit voltage in the balancedcondition.

A method of obtaining a saturated polarization as a saturated value ofvoltage drop of the terminal voltage by the internal resistance otherthan the direct-current resistance will be described.

An energy of the battery to be discharged actually for a load is acapacity remained by subtracting a capacity corresponding to the voltagedrop generated in the battery during discharging, that is the capacityto be not dischargeable by the internal resistance of the battery, fromthe charged capacity (product of the current and the time) correspondingto the value of open-circuit voltage of the battery.

The voltage drop generated in the battery during discharging to satisfya condition of detecting the saturated polarization can be divided to apart of the voltage drop (IR drop shown in Figure) by the direct-currentresistance of the battery and a part of the voltage drop by the otherinternal resistance than the direct-current resistance (saturatedpolarization shown in Figure) as shown in FIG. 9.

The above voltage drop by the internal resistance other than thedirect-current resistance of the battery does not increase and decreasesynchronously with the discharge current. Therefore, in the battery,which the voltage drop by the direct-current resistance to beproportional to the discharge current, by obtaining the direct-currentresistance by the above method, a timing when the voltage drop by thepolarization reaches to the maximum value, that is the saturated value,must be detected.

From the discharge current and the terminal voltage of the batterymeasured at intervals in a short time discharge from the balancedcondition, a following approximate equation of the characteristics ofcurrent-voltage can be given.V=a*I ² +b*I+c  (12)

The above terminal voltage V of the battery can be also shown as followsby the sum of a part of the voltage drop by the direct-currentresistance Rn and a part of the voltage drop V_(R) (voltage drop bypolarization) by the internal resistance other than the part by thedirect-current resistance.V=c−(Rn*I+V _(R))  (13)

The following equation can be led from the equations (12) and (13).a*I+B*I=−(Rn*I+V _(R))  (14)

By differentiating the above equation (14), the change ratio dV_(R)/dIof the voltage drop by internal resistance other than the direct-currentresistance of the battery can be obtained.dV _(R) /dI=−2a*I−b−Rn  (15)

When the above change ratio dV_(R)/dI becomes to zero, the dischargecurrent corresponds to a saturated current of the terminal voltage dropIpol (=−(Rn+b)/2a) when the part by internal resistance other than thedirect-current resistance of the battery becomes the maximum value (thesaturated value).

When the discharge is from the balanced condition, by assigning theobtained saturated current of the terminal voltage drop Ipol as thedischarge current I and the direct-current resistance Rn together intothe equation (14), an obtained voltage drop V_(R)(=−a*Ipol²−b*Ipol−Rn*Ipol) by polarization is defined as a saturatedpolarization V_(R)pol.

After obtaining the saturated polarization V_(R)pol showing thesaturated value of the voltage drop by the internal resistance otherthan the direct-current resistance, SOH1 is obtained by using thedirect-current resistance Rn and the saturated polarization V_(R)pol.

SOH1 can be given by calculating a ratio of the dischargeable capacityADC, which is a value of subtracting the capacity not to be dischargedby the internal resistance from the charge capacity, against a chargecapacity SOC as an electric charge in the battery.SOH1=ADC/SOC*100[%]

A voltage value V_(ADC) corresponding to the above dischargeablecapacity ADC can be obtained as follows.V _(ADC) ═OCV0−Rn*Ip−V _(R) pol

herein, OCVn is an open-circuit voltage of the battery and Ip is thepeak current of the discharge. As mentioned above, by subtractingV_(R)pol, the lowest voltage V_(ADC) when the discharge continues can beobtained.

From the voltage V_(ADC) obtained above, the dischargeable capacity ADCis given by a following converting equation in a voltage system.ADC={(V _(ADC) −Ve)/(OCVf−OCVe)}*100[%]Ve=OCVf−I*R _(ref)

OCVf is an open-circuit voltage at a full-charge of a new battery, andOCVe is an open-circuit voltage at the end of discharge of the newbattery. R_(ref) is a design value of the direct-current resistance(ohmic resistance) of the new battery for the open-circuit voltage OCVn,that is the capacity of full-charge of the battery at start ofdischarge.

SOC can be given by the following equation.SOC={(OCVn−OCVe)/(OCVf−OCVe)}*100[%]

Therefore, the above SOH1 can be given by assigning the direct-currentresistance Rn of the battery and the saturated polarization V_(R)pol tothe following equation.SOH1={(V _(ADC) −Ve)/(OCVn−OCVe)}*100[%]  (16)

The method of calculating the second deterioration degree (SOH2) bydecrease of the active material in the battery causing the decrease ofthe charge capacity of the battery will be described.

SOH2 is obtained based on decreased value of the capacity of thefull-charge at any time against the capacity of the full-charge of thenew battery.

Usually, regarding the battery by design, that is the new battery, theopen-circuit voltage at full-charge OCVf and the voltage at the end ofthe discharge OCVe to be shown with a unit V (voltage), and an initialelectric charge, shown with Ah (Ampere*time), which can be stored fromthe open-circuit voltage at full-charge to the voltage at the end ofdischarge can be predetermined. The above open-circuit voltage atfull-charge OCVf corresponds to a capacity at full-charge of the newbattery.

Therefore, if the open-circuit voltage at full-charge at any time of thebattery OCVd is known, the decreased value of the capacity of thefull-charge at any time against the capacity of the full-charge of thenew battery can be given based on the OCVd and OCVf predetermined above.

A method of detecting OCVd will be described. In a vehicle, the batteryis usually used in an in-between charge condition not to reach thefull-charge condition. For improving a deterioration generated byrepeating charge/discharge in the in-between charge condition, thebattery is charged periodically to be in the full-charge condition forrefreshing. OCVd can be detected by monitoring a decrease of an effectof charge at such refresh charge.

When the charge condition of the battery approaches to the full-chargecondition in the refresh charge, the effect of charge is decreased byincrease of gasification resistance caused by gassing (for example,decreased to near zero). Therefore, by calculating the effect of chargeperiodically in the refresh charge, and by monitoring the decrease ofthe effect of charge calculated as shown above, a time point of thebattery reaching the full-charge condition can be known, so that theopen-circuit voltage at the time point can be detected as OCVd.

Relation between the open-circuit voltage and the electric charge in thebattery is changed comparing with new battery by decrease of anelectrolyte. Therefore, by compensating OCVd with the value of the abovechange, the full-charge capacity and the second deterioration degree canbe obtained more securely.

The battery condition monitor acting the method of monitoring thebattery condition according to the present invention are described withreference to FIG. 1 showing a schematic block diagram of the monitor.

FIG. 1 is a block diagram of one embodiment of a battery conditionmonitor to perform the method of calculating the dischargeable capacityand the method of monitoring the battery condition according to thepresent invention. The battery condition monitor of the embodiment shownwith mark 1 in FIG. 1 is installed in a hybrid vehicle with a motorgenerator 5 added on an engine 3.

In the hybrid vehicle, an output power of the engine 3 is transmittedfrom a drive shaft 7 through a differential case 9 to a wheel 11 fornormal driving. At high load condition, the motor generator 5 isperformed as a motor by electric power of a battery 13 and an output ofthe motor generator 5 added on the output of the engine 3 is transmittedfrom the drive shaft 7 to the wheel 11 for assist driving.

In the hybrid vehicle, the motor generator 5 is performed as a generatorat decelerating and breaking to convert kinetic energy to electricenergy for charging the battery 13 installed in the hybrid vehicle forsupplying electric power to various loads.

The motor generator 5 is used as a self-starting motor to rotate aflywheel of the engine 3 forcibly when the engine 3 is started byturning a starter switch (not shown) ON.

The battery condition monitor 1 includes a current sensor 15 fordetecting a discharge current I of the battery 13 for the motorgenerator 5 performing as the motor of assist driving and theself-starting motor and a charging current from the motor generator 5 asa generator to the battery 13, and a voltage sensor 17 connected inparallel with the battery 13 to have an infinitely large resistance fordetecting a terminal voltage of the battery 13.

The current sensor 15 and the voltage sensor 17 mentioned above areprovided in a circuit to be closed by turning an ignition switch ON.

The battery condition monitor 1 includes a microcomputer 23 in whichoutputs of the current sensor 15 and the voltage sensor 17 are inputtedafter A/D converted at an interface circuit 21 (shown by I/F hereafter),and includes furthermore a nonvolatile memory (NVM) 25.

The microcomputer 23 has a CPU 23 a, a RAM 23 b, a ROM 23 c. The RAM 23b, the ROM 23 c and the I/F 21 are connected with the CPU 23 a, and asignal of ON/OFF of the ignition switch (not shown) is inputted into theCPU 23 a.

The RAM 23 b has a data area for storing various data and a work area tobe used for various processing work. In the ROM 23 c, a control programto make the CPU 23 a operate various processing is stored.

SOH1 and SOH2 of the battery 13 is detected by the microcomputer 23performing various detection at discharge mentioned above based on theoutputs of the current sensor 15 and the voltage sensor 17. Thus, themicrocomputer 23 performs as the first deterioration detector and thesecond deterioration detector. The microcomputer 23 also monitors thecondition of the battery 13.

According to the above battery condition monitor, the deteriorationincluding the irreversible and reversible deterioration can be monitoredby SOH1, and the irreversible deterioration can be monitored. Therefore,by monitoring the battery condition based on the both of SOH1 and SOH2,the battery condition can be securely monitored.

EFFECT OF INVENTION

As mentioned above, according to the present invention as claimed inclaims 1 and 4, deterioration including the irreversible and reversibledeterioration can be monitored by the first deterioration degree, andthe irreversible deterioration can be monitored by the seconddeterioration degree. Therefore, by monitoring the battery conditionbased on the first and second deterioration degrees, a battery conditionmonitor which can monitor securely the battery condition and a methodthereof can be provided.

According to the present invention as claimed in claim 2, only bydetecting the discharge current and the terminal voltage of the batteryin various discharge, and processing the detected results, thedirect-current resistance and the saturated polarization can beobtained. Therefore, the first deterioration degree can be detected inuse of the battery. By obtaining the saturated polarization, the firstdeterioration degree at the point in which the dischargeable capacitydecreases to the lowest when the discharge continues. Thereby, thebattery condition monitor, which can monitor more securely the batterycondition, can be provided.

According to the present invention as claimed in claim 3, by obtainingthe value of decrease of the full-charge capacity, the battery conditionmonitor, which can obtain the second deterioration degree easily, can beprovided.

1. A battery condition monitor for monitoring a condition of a battery,comprising: a first deterioration detector for detecting a firstdeterioration degree cause by increase of an internal resistance of thebattery; and a second deterioration detector for detecting a seconddeterioration degree caused by decrease of active material of thebattery to cause decrease of a charge capacity of the battery, whereinthe condition of the battery is monitored based on the firstdeterioration degree and the second deterioration degree.
 2. The batterycondition monitor according to claim 1, wherein the first deteriorationdetector obtains a direct-current resistance of the battery based on adischarge current and terminal voltage of the battery detected in ahigh-rate discharging, and obtains a saturated polarization, as asaturated value of a voltage drop by the internal resistance other thanthe direct-current resistance, based on the discharge current and theterminal voltage of the battery detected in discharging, and thedirect-current resistance of the battery, and detects the firstdeterioration degree based on the direct-current resistance and thesaturated polarization.
 3. The battery condition monitor according toclaim 1, wherein the second deterioration detector detects the seconddeterioration based on a decreasing value of the charge capacity atfull-charge of the battery at any time corresponding to the chargecapacity at full-charge of a new battery.
 4. A method of monitoring abattery condition comprising a step of monitoring the battery conditionbased on a first deterioration degree caused by increase of an internalresistance of the battery and a second deterioration degree indicating adecreasing value of active material of the battery to cause decrease ofa charge capacity of the battery.
 5. The battery condition monitoraccording to claim 2, wherein the second deterioration detector detectsthe second deterioration based on a decreasing value of the chargecapacity at full-charge of the battery at any time corresponding to thecharge capacity at full-charge of a new battery.